Photographic color reversal process



United States Patent 3,259,497 PHOTOGRAPHIC COLOR REVERSAL PROCESS Ren von Wartburg, Basel, Switzerland, assiguor to Ciba Limited, Basel, Switzerland, a Swiss companyv No Drawing. Filed Aug. 29, 1962, Ser. No. 220,155 Claims priority, application Switzerland, Sept. 6, 1961, 10,340/ 61 7 Claims. (Cl. 9653) The silver dye bleaching process, which is based on the decomposition of certain dyes by metallic silver is used for producing an opposite color image from a silver image. Accordingly, when a material is processed in the conventional manner by the silver dye bleaching method, a positive master gives a negative silver image and finally a positive color print is formed. It has already been proposed that for the production of a positive color print from a negative master, the primary positive silver image should be converted by reversal development into a negative silver image, and a positive color image should be made from it by the dye bleaching method. In this context the terms negative and positive should be interpreted relatively, since more generally speaking, the result of the silver dye bleaching process including a silver reversal development may be characterized in that an opposite color print is obtained from a master.

The silver reversal development involved consists in removing the primarily formed silver image and reducing the silver halide, that has not been reduced by the primary development, to metallic silver. The removal of the primarily developed silver is conventionally carried out in an oxidation bath, for example, a bath containing an aqueous solution of a bichromate and sulfuric acid.

It is known that strong oxidants decompose many of the dyes used in the silver dye bleaching process. Attempts have therefore been made to replace the strong oxidation bath by weaker oxidants which convert the silver corresponding to the primary image into silver chloride or silver thiocyanate. These latter compounds are more readily soluble than the undeveloped silver bromide, and are separated by treatment with a concentrated alkali metal chloride solution. However, this procedure, especially in the case of multi-layer materials, does not cause complete separation of the readily soluble silver salt from the more sparingly soluble silver salt. Many weak oxidants that do not appreciably attack the dye, moreover, do not completely remove the primary silver image. An attempt has been made to dispense with the strong oxidation bath and to bleach the dye with stannite in the presence of unreduced silver halide, but the great majority of dyes available for the silver dye bleaching process cannot be bleached by the said method.

The present invention is based on the observation that dyes which are attacked by strong oxidation baths capable of dissolving metallic silver can withstand these baths when treated in a suitable manner. When the oxidation of silver is carried out in the presence of an organic base, the dye is rendered passive towards the action of the oxidant, without reducing the possibility of oxidizing metallic silver.

The present invention provides a process for the production of a color image opposite to the master by the silver dye bleaching process in a single-layer or multilayer material containing at least one silver halide emulsion and at least one dye which is sensitive to oxidation, can be bleached by the silver bleaching process and is resistant to diffusion, by exposure, primary development, removal of the primarily developed silver in a strong oxidation bath, secondary development, dye bleaching and the removal of any residual silver. According to the present process, the removal of the primarily developed Patented July 5, 1966 silver is carried out in the presence of an organic compound containing at least one basic nitrogen atom, viz. of an organic base'or a salt thereof, whereby the dye is protected from the attack of the strong oxidation bath. The invention further includes novel oxidation baths for carrying out the present process.

Preferably, organic bases or their salts that are used in the present process resemble those which are used as stains and for improving the fastness to washing. The use of such precipitants in the preparation of dyed emulsions or in photographic baths is known. The purpose of their addition is generally to reduce the migration tendency of the dyes, so that difiusing dyes can be converted into a diffusion-resistant form.

However, it has not previously been proposed to use such bases together with or prior to a strong oxidation bath in a reversal process, and there was of course no reason why the bases should be used in connection with dyes that were as such diffusion-resistant.

In contradistinction to the known methods, the bases or their salts are used according to the present process to render the dyes stable towards the oxidant. Layers are used, having the dyes incorporated with the layer colloids, such dyes being diffusion-resistant, so that they require no precipitants to anchor them in the layer. According to the invention, the bases or their salts are incorporated, for example, with the molten emulsion before casting, or are added to one of the treatment baths, and in such cases they cause no substantial increase in the diffusion stability of the dyes. Thus, the bases or their salts may be present, for example, in the developer or in a stop bath following after the developer, or in a special bath following after the stop bath, or in the oxidation bath itself. It is advantageous to add a salt of the base to the oxidation bath, or to a bath immediately preceding the oxidation bath,- and if desired an intermediate washing operation can be carried out. In many cases, an optimum elfe'ct may be achieved when a bath preceding the oxidation bath contains a base and, in addition to this, the oxidation bath itself contains the identical or a different base. The addition of the bases to the bath (and especially to a bath following after the developer) has the advantage that in such a case, the photosensitive emulsions are not encumbered with additional substances which would have a desensitizing, coagulating or in other ways disturbing effect, and that the silver development itself is not obstructed. Another advantage is that it is possible to incorporate with the baths a larger excess of readily diffusing bases or salts thereof, and that it is easy to wash this excess out again after the oxidation bath. Accordingly, the material contains an increased amount of base during its treatment in the oxidation bath. It goes without saying that when selecting bases to be dissolved in the oxidation bath itself only those which do not form insoluble salts with the anions present in this bath, can be 'used. Apart frorn'the aforementioned baths, and the necessary intermediate rinses, other baths may be interposed. The organic bases and salts thereof which are suitable for use in the emulsion or preferably in the baths, are for example quaternary nitrogen compounds, more especially those derived from bicyclic bases, or derivatives of guanidine, for example, biguanides.

As examples, the following bases and salts may be mentioned:

Ethylenediamine,

Benztriazole,

Diphenyl-4:4'-dibiguanide hydrochloride or acetate, Dicyandiamide,

p-naphthylbiguanide acetate,

urgent demand for improved processes for the production of positive prints from the said negatives, for example, prints to be viewed in refiected light. The present process is also important because, amongst the vast number of dyes proposed for use in the silver dye bleaching process, only a few satisfy the requirements insofar as spectral purity, ease for bleaching, fastness to light, fastness to difiusion etc. are concerned, so that when dyes are selected according to their oxidation resistance, other important factors are neglected. According to the present invention it is also possible to use in a dye bleaching reversal process, dyes that are not only fast to oxidation but also satisfy all other demands.

The following examples illustrate the invention:

Example 1 A double-weight baryta photographic printing paper is coated with a silver bromide emulsion sensitized to red which contains the cyan dye of the formula HO NH H N' (I) H H O O (I) C 3 2 l S 0311 H 0 3 are most advantageously incorporated in the oxidation bath.

The oxidation baths contain a strong oxidant in a I OH taining hexavalent chromium compounds in a concentration as is conventionally used to remove primary silver images in the reversal process. The efficiency of such a bath can be increased by adding a surface active agent which has the effect of promoting the readiness of the metallic silver to undergo oxidation but not the ease of decomposition of the dye, so that the time taken by the treatment can be shortened. Suitable surface active agents are wetting agents containing fluorine, more especially fluorinated aliphatic carboxylic acids and salts thereof. Good results are obtained with the product marketed under the registered Trademark PC-95 by Minnesota Mining & Mfg. Corp, St. Paul, Minnesota, U.S.A.

The treatment with the base or a salt thereof improves the stability of the dyes that are unstable in oxidation baths, but does not impair any per se oxidation-resistant dyes that may be present in other layers. It is easy to discover the oxidation resistance of a dye, and as far as is necessary the best suited treatment for improving the oxidation resistance according to the present process, by preliminary tests in each case.

In color photography, the negative-positive processes are gaining more and more ground, so that there is an Sulfuric acid is particularly suitable for 40 and then with a thin coating of gelatine. The latter is covered with a silver bromide emulsion sensitized to green, containing a magenta dye of the formula HOQS HO which is then covered with a gelatine layer containing a yellow filter dye of the formula H30 O so followed by an unsensitized emulsion containing a yellow dye of the formula Two strips of this multi-pack material are exposed in a sensitometer under Wratten filters 29, 16+61 and 49+28.

The layers are then developed for 15 minutes in a developer containing the following ingredients:

Potassium iodide 0.01 Water to make 1 liter.

The development is then stopped in a bath of acetic acid of 3% strength.

To remove the silver formed, test strip 1 is bathed for 4 minutes in the following solution.

Sodium bichromate, g. 5 Sulfuric acid of 98% strength, ml 5 Water to make 1 liter.

consisting of:

while strip 2 is treated in a bath Potassium bichromate, g. 5

Sulfuric acid of 98% strength, ml 5 3-methyl-2-methylmercapto benzthiazolium methylsulfate, g. 5

Water to make 1 liter.

G. Metol 3 Anhydrous sodium sulfite 64 Hydroquinone 12 Anhydrous sodium carbonate 60 Potassium bromide 2 Water to make 1 liter.

The development is then stopped in an acetic acid bath of 3% strength and the strips are fixed in an acid fixing bath.

The strips are then washed with water and introduced into a dye bleaching bath of the following composition:

Potassium bromide, g 50 Thiourea, g. 30 Hydrochloric acid of 37% strength, ml 40 2-amino-S-hydroxyphenazine, mg. 1

Water to make 1 liter.

After a short washing in water, the residual silver is converted into silver chloride in a bath of the following composition:

Sodium chloride, g 100 Crystalline copper sulfate, g. 100 Hydrochloric acid of 37% strength, ml 50 Water to make 1 liter.

Example 2 A strip of the multi-pack material used in Example 1 is exposed and developed as described in the Example 1. After having been developed, the strip is immersed in a stop bath of the following composition:

Acetic acid, ml. Sodium acetate, g. Diphenyl-4:4'-dibiguanide acetate, g. 3 Water to make 1 liter.

After an intermediate rinse, the silver is bleached out in a bath of the following composition:

Potassium bichromate, g 5 Sulfuric acid, ml. 2 1:2-dimethyl quinolinium methylsulfate, g. 1.5 PC-95, g. 0.2

Water to make 1 liter.

The strip is then further processed as described in Example 1.

After drying, the wedge exposed under filter 16+61 displays the magenta dye in the same saturated tint and brilliance as it had before incorporation with the emulsion.

Example 3 The method described in Example 1 is used except that for test strip 2, an oxidation bath is used which con- 6 tains instead of 3-methyl-2-methylmercapto benzthiazolium methylsulfate, 5 g. of one of. the following compounds:

lz2-dimethyl quinolinium methylsulfate,

2: 3-dimethyl benzthiazolium methylsulfate, l-methyl quinolinium methylsulfate,

Ethyl pyridinium bromide,

1:2-dimethyl pyridinium methylsulfate, or Benzyl trimethyl ammonium chloride.

Example 4 The stop bath is prepared as described in Example 2 except that instead of using diphenyl-4:4-dibiguanide acetate, 3 g. of one of the following compounds are used: Diphenyl-4:4'-dibiguanide chloride, fi-naphthyl biguanide acetate,

Dicyandiamide, Ethylenediamine, or Benztriazole.

Also in this case, the magenta dye is of a well saturated tint.

Example 5 The process described in Example 2 is used, except that before casting the layer containing the magenta dye diphenyl-4:4-dibiguanide acetate is added to it, and the stop bath does not contain this substance. After processing and drying, it is observed that the magenta dye has not suffered any damage in the oxidation bath.

What is claimed is:

1. In a process for the production of a color image that is opposite to the master by the silver dye bleaching method in an at least single-layer material, which contains at least one silver halide emulsion and at least one dye which is sensitive to oxidation, fast to diffusion, and can be bleached by the silver dye bleaching process, by exposure, primary development, removal of the primarily developed silver in an oxidation bath containing sulfuric acid and an oxidant selected from the group of heptavalent manganese compounds, hexavalent chromium compounds, hydrogen peroxide derivatives and tervalent cerium compounds, secondary development, dye bleaching and removal of the residual silver, the step which comprises carrying out the removal of the primarily developed silver in the presence of a water soluble organic compound containing at least one basic nitrogen atom selected from the group consisting of ethylenediamine, benztriazole derivatives, guanidine derivatives, biguanide derivatives, pyridine derivatives, quinoline derivatives, benzthiazole derivatives, piperidine derivatives, benzyl trimethyl ammonium chloride and tetra-n-butyl-ammonium bromide.

2. In a process as claimed in claim 1, the step which comprises incorporating the water-soluble organic compound containing at least one basic nitrogen atom with the emulsion prior to casting.

3. In a process as claimed in claim 1, the step which comprises adding the water-soluble organic compound containing at least one basic nitrogen atom to a photographic bath.

4. In a process as claimed in claim 1, the step which comprises adding the water-soluble organic compound containing at least one basic nitrogen atom to a photographic bath, in which the photographic material is treated after the primary development and before the oxidation bath.

5. In a process as claimed in claim 1, the step which comprises adding the water-soluble organic compound containing at least one basic nitrogen atom to the strong oxidation bath.

6. In a process as claimed in claim 1, the step which comprises adding diphenyl-4:4-dibiguanide to a stop bath, which is employed after the primary development of the silver and before the oxidation bath.

7 7. In a process as claimed in claim 1,the step which comprises adding 1:2-dimethy1-quinolinium methylsulfate to the oxidation bath.

References Cited by the Examiner UNITED STATES PATENTS 2,184,022 12/1939 Seymour 96-60 2,195,419 4/1940 McQueen et al 96-60 2,205,755 6/1940 Von Biehler 96-20 2,229,891 1/1941 Ham 96-60 2,262,723 11/1941 Ham 96-60 Weher 96-59 Sprung 96-60 Brunner et al 96-60 Friedman 96-20 Sprung 96-20 Sprung 96-20 Mueller 96-20 Gaspar 96-60 Lassig et a1 96-60 10 NORMAN G. TORCHIN, Primary Examiner.

A. D. RICCI, C. E. DAVIS, Assistant Examiners. 

1. IN A PROCESS FOR THE PRODUCTION OF A COLOR IMAGE THAT IS OPPOSITE TO THE MASTER BY THE SILVER DYE BLEACHING METHOD IN AN AT LEAST SINGLE-LAYER MATERIAL, WHICH CONTAINS AT LEAST ONE SILVER HALIDE EMULSION AND AT LEAST ONE DYE WHICH IS SENSITIVE TO OXIDATION, FAST TO DIFFUSION, AND CAN BE BLEACHED BY THE SILVER DYE BLEACHING PROCESS, BY EXPOSURE, PRIMARY DEVELOPMENT, REMOVAL OF THE PRIMARILY DEVELOPED SILVER IN AN OXIDATION BATH CONTAINING SULFURIC ACID AND AN OXIDANT SELECTED FROM THE GROUP OF HEPTAVALENT MANGANESE COMPOUNDS, HEXAVALENT CHROMIUM COMPOUNDS, HYDROGEN PEROXIDE DERIVATIVES AND TERVALENT CERIUM COMPOUNDS, SECONDARY DEVELOPMENT, DYE BLEACHING AND REMOVAL OF THE RESIDUAL SILVER, THE STEP WHICH COMPRISES CARRYING OUT THE REMOVAL OF THE PRIMARILY DEVELOPED SILVER IN THE PRESENCE OF A WATER SOLUBLE ORGANIC COMPOUND CONTAINING AT LEAST ONE BASIC NITROGEN ATOM SELECTED FROM THE GROUP CONSISTING OF ETHYLENEDIAMINE, BENZTRIAZOLE DERIVATIVES, GUANIDINE DERIVATIVES, BIGUANIDE DERIVATIVES, PYRIDINE DERIVATIVES, QUINOLINE DERIVATIVES, BENZTHIAZOLE DERIVATIVES, PIPERIDINE DERIVATIVES, BENZYL TRIMETHYL AMMONIUM CHLORIDE AND TETRA-N-BUTYL-AMMONIUM BROMIDE. 